Switch actuating and control mechanism for vacuum type electric circuit interrupters with lost-motion and bellows biasing means



06L 19.70 H. A. FOHRHALTZ 3,532,842

SWITCH ACTUATING AND CONTRO L MECHANISM FOR VACUUM TYPE ELECTRIC CIRCUIT INTERRUPTERS WITH LOST-MOTION AND BELLOWS BIASING MEANS Filed Aug. 5, 1966 v 4 Sheets-Sheet l 29mm) A. FoHRHALTz, M m

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SWITCH ACTUATING AND CONTROL MECHANISM FOR VACUUM TYPE ELECTRIC CIRCUIT INTERR UPTERS WITH LOST-MOTION AND BELLOWS BIASING MEANS Filed Aug. 5, 1966 4 Sheets-Sheet 2 I 9' H I J6 J8 g 36 i I I r I; .lI h: O O 1-15.; I 5::

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Oct. 6, 1970 H. A. FOHRHALTZ 3,532,842

SWITCH ACTUATING AND CONTROL MECHANISM FOR VACUUM TYPE ELECTRIC CIRCUIT INTERRUPTERS WITH LOST-MOTION AND BELLOWS BIASING MEANS Filed Aug. 5. 1966 4 Sheets-Sheet, 5

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HOWARD AFOHRHALTZ, By M 7'7'0R/VEY Oct. 6, 1970 C H A. FOHRHALTZ 3,532,842

SWITCH ACTUATING AND COIi'I'ROL MECHANISM FOR VACUUM TYPE ELECTRIC CIRCUIT INTERRUPTERS WITH LOST-MOTION AND BELLOWS BIASING MEANS Filed Aug. 5. 1966 4 Sheets-Sheet 4 \\\lIII//// //v VENTOR. HOWARD A. fbHRHALTz,

TORNEY United States Patent 3,532,842 SWITCH ACTUATING AND CONTROL MECHA- NISM FOR VACUUM TYPE ELECTRIC CIRCUIT INTERRUPTERS WITH LOST-MOTION AND BELLOWS BIASING MEANS Howard A. Fohrhaltz, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Filed Aug. 5, 1966, Ser. No. 570,485 Int. Cl. H01h 33/66 U.S. Cl. 200-144 5 Claims ABSTRACT OF THE DISCLOSURE The application discloses an improved switch actuating mechanism having discrete controlled opening and closing speeds especially applicable to the operation of vacuum interrupting devices biased to circuit closing position. Preferably the movable contact member of the Vacuum interrupter is fixed to a flexible portion of the vacuum interrupter envelope, and is biased to circuit closing position by differential pressure. A switch actuating member biased to contact opening position by a strong op erating spring is loosely coupled to the movable contact member through a lost-motion connection which permits overtravel of the actuating member in its contact-closing direction. In switch opening operation the overtravel of the switch actuating member permits rapid contact opening by impact of the switch actuating member against the movable switch member. In reclosing operation the closing bias of the movable switch member and positive drive of the switch actuating member acts to restrain the movable switch member to a desired relatively slow reclosing speed. For operation of the vacuum interrupt ing device under oil or other liquid, pressure relief passages are provided to permit egress of the liquid from the bellows and thus limit stress on the bellows in rapid switch-opening operation.

My invention relates to switch actuating and control mechanism particularly applicable to vaccum type electric circuit interrupters. This improved mechanism is suitable for operation totally immersed in dielectric liquid and is therefore especially useful with vacuum interrupters used as arcing contact devices in transformer load tap changing apparatus.

Stepping-contact type load tap changers for large liquid-immersed electric power transformers, reactors and the like ordinarily include an arcing duty current interrupting switch which is typically located in a separate air or liquid-filled compartment to avoid contamination of the main body of transformer liquid. To accommodate the mechanical interconnection of the arcing switch with the stepping contacts and other switches in a tap-changing apparatus, it has therefore been customary to locate the entire tap-changing apparatus in the separate compartment.

It is desirable for several reasons to utilize a vacuum type interrupter as the arcing duty switch in a load tap changer. In high voltage apparatus where the tap changing contacts must be immersed in dielectric fluid, it is possible to locate the entire tap-changing apparatus directly within the main tank and immersed in the main body of oil or other dielectric fluid. It is, therefore, possible to avoid the considerable expense of a separate fluidfilled tank and numerous tap connections between this and the main tank. In lower voltage apparatus where liquid immersion of the tap changer is not necessary, the same apparatus can be used inside or outside the main tank as other design parameters may suggest.

Transformer load tap-changing apparatus, especially when automatically controlled for voltage or current regulation, is called upon to perform its operation at a high repetition rate. A vacuum type are interrupter used in such apparatus therefore operates very frequently and must have an operating lifemeasured in many thousands, and preferably millions, of switching operations. When such a vacuum interrupting device is located in the main tank of liquid-immersed transformer or the like, it is especially important that the device function dependably over a long period of time because of the difliculty and expense of exposing it for maintenance.

To ensure long operating life of a vacuum operating device, it is essential that the opening and closing speeds of its contacts be carefully controlled to minimize arcing, and that the switch parts be protected from high mechanical stress to avoid fatigue of the metal parts. Proper contact operating speed presents an additional problem in that opening speed must be relatively high to ensure current interruption at the first current zero with minimum arcing, while contact closing speed must be considerably lower to avoid contact bounce and needless arcing. Another problem related to frequency and speed of contact operation arises from the usual use of an expansible metallic bellows to mount and seal the movable contact in a vacuum interrupting device. Where operating duty is highly repetitive, it is particularly important that this bellows be protected from high stress in operation. This problem is particularly acute when the interrupter is operated in a liquid-immersed location. When an incompressible ambient liquid fills the interior of the bellows, high speed operation may be limited and the bellows may be overstressed by the pressures created.

Accordingly it is a principal object of my invention to provide improved contact actuating and control means for a vacuum type electric circuit interrupting device designed to provide long operating life and thereby to facilitate utilization in liquid-immersed locations and other locations not readily accessible.

It is another object of my invention to provide a vacuum interrupting device and operating mechanism therefore especially adapted for use as an oil-immersed arcing duty switch in transformer tap-changing under load apparatus.

Still another object of my invention is to provide contact actuating and control apparatus for a vacuum type circuit interrupting device designed to minimize stress on the switch parts and predetermine opening and closing speeds of the contacts whether the ambient medium be gaseous or liquid.

A still further object of the invention is to provide a switch actuating mechanism operable by a reversible operating member to open a pair of cooperating switch contacts at high speed and reclose at slow speed irresponsive of the direction of movement of the reversible operating member.

In carrying out my invention in one preferred embodiment, I locate a vacuum type circuit interrupting device under oil in a transformer housing and connect it as an arcing duty switch for actuation in proper sequence by a reversible tap-changing motor. A reversible switch operating cam driven by the motor moves a switch operating rod in one direction to open the vacuum interrupter and in the opposite direction to reclose. A movable switch actuating member spring-pressed to circuit opening position is connected to the movable switch contact by a lost-motion linkage and normally latched in an overtravel position beyond its circuit closing position. The movable switch contact itself is biased to closed position to follow the switch actuating member in closing movement but its bias is overcome by the actuating spring. In opening operation, therefore, unlatching of the actuating member resulting from movement of the operating cam in either direction releases the actuating spring to open the contacts rapidly by impact action 'at the end of overtravel movement of the switch member. In closing operation the movable contact is returned to engaged position at a predetermined slower rate determined by positive drive of the actuating member to latching position. To facilitate contact opening operation at predetermined high speed without unduly stressing the expansible metallic bellows in the interrupting device, especially when operated in an oil-immersed location, I provide a metering orifice of ample size which, if desired can be calculated to control the bellows by dashpot action.

My invention will be more fully understood and its various objects and advantages further appreciated by referring now to the following detailed specification taken in conjunction with the accompanying drawing wherein:

FIG. 1 is a schematic circuit diagram of a transformer load tap-changing apparatus including a vacuum type arc interrupting switch.

FIG. 2 is a front elevational view of a cam-operated vacuum interrupting switch suitable for use in the circuit location shown at FIG. 1 and including lost-motion switch actuating and control mechanism embodying my invention.

FIG. 3 is a side elevational view of the cam-operated vacuum interrupting device and actuating mechanism shown at FIG. 2.

FIG. 4 is an exploded perspective view of the switch apparatus shown in FIGS. 2 and 3.

FIG. 5 is a fragmentary cross-sectional view of the vacuum interrupting device and its mounting, taken along the line 5-5 of FIG. 3 and showing particularly the movable contact mounting.

FIG. 6 is a cross-sectional view of the latching mechanism taken along the line 6-6 of FIG. 2, and

FIG. 7 is a fragmentary perspective view of a modlfied form of the switch actuating mechanism shown at FIGS. 2, 3 and 4.

Referring now to the drawing, I have shown at FIG. 1 a schematic circuit diagram of a transformer load tap changing apparatus of a type to which my improved switching apparatus is especially adapted. The transformer itself comprises a pair of main windings 2, 3 and an auxiliary control power winding 4, all of which are inductively coupled and preferably immersed in a dielectric fluid such as oil or askarel. The main winding 3 is provided with a plurality of selectable voltage taps each having a tap terminal contact 5. A selected one of the tap terminals 5 is adapted to be connected through a load tap-charging apparatus g to a line conductor 7.

The load tap-changing apparatus designated generally by the reference numeral Q includes a pair of contact fingers 8, 9 of a double finger non-arcing duty tap selector switch movable in step-by-step manner along the tap contacts 5, a pair of current limiting reactors 10, 11 associated respectively with the contact fingers 8 and 9, a pair of non-arcing duty transfer switches 12 and 13, and a vacuum type arc interrupting switch 14. A reversible cycle timer including a driving motor is provided for controlling the operation of the foregoing transfer, interrupting and selector switches. The motor 15 is controlled by a voltage regulating relay 16, and the entire apparatus except the voltage regulating relay is preferably immersed in the main body of dielectric fluid surrounding the transformer windings 2 and 3.

The tap selector circuit of the apparatus Q is of a wellknown type and is similar to that illustrated in Pat. 3,206,580McCarty. The circuit provides two parallel current paths, or branch circuits, between any selected tap terminal 5 and the line conductor 7, each parallel path including one of the tap selector fingers 8, 9 in series with one of the reactors 10, 11 and one of the transfer switches 12, 13. The arcing duty vacuum interrupting device 14 is connected between the parallel branch circuits with the transfer switches 12, 13 in series circuit 4 relation directly across the arcing contacts of the vacuum switch.

The timing motor 15 is selectably operable in either direction under the control of the voltage regualting relay 16 to effect sequential stepping movement of the tap selector fingers 8, 9 progressively in either direction along the group of transformer tap terminals 5. The reversible timing motor 15 drives a switch operating cam 20 coupled to actuate the transfer switches 12, 13, a switch operating cam 21 coupled to actuate the arcing duty vacuum switch 14, and intermittent motion transmitting device, such as a Geneva gear 22, coupled to actuate the selector fingers 8, 9. The switch operating cams 20, 21 and the Geneva gear 22 for the tap selector fingers are arranged to actuate the selector fingers and the several switches in appropriate sequential relation in any cycle of tap changing movement. The cam 20 has a circumferential cam slot 25 having a single axially offset section 25a as shown at FIG. 1. The cam 21 has a circumferential cam; slot .26 provided at diametrically opposite points with axially offset sections 26a (FIGS. 2 and 4) only one of which is shown at FIG. 1. The slot sections 26a are angularly shorter than the slot section 25a, and one is centrally located with respect to slot section 25a.

A typical single cycle of operation of the tap-changing apparatus described above is as follows. If the cycle timing motor 15 is energized for operation in either direction through the voltage regulating relay 16, one of the selector switches 12, 13' is first opened while the other remains closed. Assuming rotation of the cams 20, 21 in the direction indicated by the arrow, it is evident that a cam follower rod 27 first opens the transfer switch 12 thereby to transfer the branch circuit through the selector finger 8 from the switch 12 to the vacuum interrupting device 14. Thereafter the cam 21 (through its diametrically opposite offset sections 26a) actuates a cam follower rod '28 to open the vacuum interrupting device 14. With the circuit through the selector finger 8 thus interrupted, the Geneva gear 22 moves the double finger ratio adjuster switch 8, 9 to the dotted position shown with the contact finger 9 remaining on the original tap terminal 5 and the contact finger 8 on the next adjacent tap terminal 5. Continued rotation of the cam 21 next recloses the vacuum interrupting device 14 and further rotation of cam 20 closes the transfer switch 12 and thereafiter actuates a cam follower 29 to open the transfer switch 13. Following opening of the transfer switch 13 the cam 21 again opens the vacuum interrupting device 14 to interrupt the branch circuit through the selector finger 9, and the Geneva gear 22 then moves the double finger selector switch to a position where both fingers 8 and 9 are again on a common tap terminal one position beyond that at which the transfer cycle was begun. To complete the transfer cycle, continued rotation of the cam 20 and 21 next reclose the vaccum interrupting switch 14 and thereafter reclose the transfer switch 13.

At FIGS. 2, 3 annd 4 I have shown a structural arrangement of the switch operating cams 20, 21, the transfer switches 12, 13 and the vacuum interrupting device 14 mounted upon a common supporting base 30 in com bination with an actuating and control mechanism for the interrupting device 14 which embodies my invention. Referring now to these figures, the cams 20 and 21 are driven through suitable gearing from a motor shaft 15a coupled to the motor 15 (not shown) and are provided with circumferential cam slots 25 and 26, respectively, axially offset in the manner previously described. The cam 20 is coupled to actuate both of the transfer switches 12, 13 through the operating rods 27 and 29, respectively, and associated cam follower levers 27a and 29a, respectively. The operating cam 21 is connected by means of the operating rod 28 and a cam follower lever 28a to control a vacuum switch actuating mechanism designated generally by the reference numeral 32.

The vacuum interrupting device 14 is illustrated generally at FIGS. 2, 3 and 4 in greater detail at FIG. 5. This device comprises a cylindrical evacuated envelope 35 containing a fixed contact member 36 and a movable contact member 37 carried by a slidable contact rod 38. The rod 38 is mounted in a suitable slide bearing 39 shown at FIG. 5. The movable contact rod 38 is sealed to the evacuated envelope 35 by means of a deformable wall portion of the envelope shown as an exp-ansible metallic bellows 40. The bellows 40 is mounted at its fixed end upon a metallic plate 41 forming a one end closure of the envelope 35 and the movable end of the bellows is sealed to the contact rod 38. The end plate 41 is centrally apertured and the aperture is closed by the bellows 40 with the bellows on the inner side of the end plate. The bellows being thus re-entrantly positioned, its interior is open to ambient fluid surrounding the switch 14.

The vacuum interrupter end plate 41 is provided with several studs 42 by means of which the switch 14 is bolted to a mounting plate 43 attached to the supporting panel 30. The moving contact bearing 39 is carried by an inwardly extending cylindrical projection 44 fixed to the mounting plate 43 and extending into the bellows 40 with appreciable clearance between the bearing projection 44 and the central aperture of the end plate 41. The mounting plate 43 is provided with a plurality of apertures 45 located peripherally about the movable switch rod 38 to provide free flow of ambient fluid into and out of the interior of the bellows 40.

It is evident that the apertures 45 in the mounting plate 43 serve as metering orifices for controlling the flow of fluid into and out of the bellows as the bellows 40 is expanded or contracted by contact movement. Preferably the orifices 45 provide relatively little resistance to the ingress or egress of anambient liquid and thus permit high speed collapse or expansion of the bellows in switching operation without unduly stressing the bellows. While the orifice 45 are thus of suflicient size to limit pressure stresses in the bellows 40, it is evident that by precise control of the area of these orifices for operation in any pre-. determined ambient fluid, the orifices may be utilized to produce a controlled dashpot action of the bellows and thus to regulate its speed of movement under certain circumstances. In my preferred switch actuating mechanism the desired high opening speed of the vacuum interrupting device is attained by a spring drive and dash pot action of the orifices 45 cooperating to limit pressure upon the bellows. The desired slower contact closing speed is produced by positive mechanical drive but, being slower, does not overstress the bellows.

As illustrated at FIGS. 2, 3 and 4, the actuating linkage 3 interposed between the vacuum interrupting device 14 and its operating cam 21 is centered around a movable switch actuating member 50 shown as an axially slidable rod. The actuating rod 50 is biased to its circuit opening position by means of a strong compression spring 51 interposed between the rod and a fixed mounting bracket 52 and is provided at its lower end with a dashpot 53 to cushion the end of its spring actuated movement. The actuating member, or rod, 50 is loosely connected through a limited lost-motion coupling to the movable contact rod 38 of the vacuum interrupter 14 and is thus capable of limited overtravel movement with respect to the movable contact member 38. The limited lost-motion coupling comprises a cup-like cage 54 fixed to the upper end of the rod 50 and a slidable rod 55 axially aligned with the rod 50 and having a shouldered lower end 55a extending into the cage 54 for relative movement with respect thereto. The rod 55, being coupled to the movable contact rod 38 through a bell crank lever 56 and thus movable in fixed synchronous relation with respect to the movable contact, may be referred to generally as a movable switch member. The relatively movable switch actuating rod 50 is coupled to the operating cam 21 through a positive drive and latch release mechanism to be described hereinafter.

Before examining the latch and drive mechanism for the actuating rod 50, it should be noted that the movable vacuum interrupter contact rod 38 and the connected bell crank lever and switch member 55 are all biased to contact closing position by the differential pressure exerted upon the switch bellows 40, one end of which is sealed to the switch rod 38. It will be understood of course that the actuating spring 51 acting upon the actuating member is sufficiently strong to overcome the contact closing bias exerted by the bellows 40. In the embodiment of my invention illustrated at FIGS. 2, 3 and 4, I have shown in addition to these opening and closing bias forces a relatively weak compression spring 57 interposed between the fixed bracket 52 and the headed end a of the switch rod 55. This compression spring 51 serves to oppose, but normally not to overcome, the closing bias of the bellows 40. The purpose of the spring 57 is to serve as a pushotf spring to separate the vacuum interrupter contacts 36 and 37 without movement of the actuating member 50 in the event that differential pressure on the bellows 40 is significantly reduced by loss of vacuum in the device 14. The pusholf spring 57 is not essential to the operation of my invention but is useful primarily in the loss of vacuum arrangement briefly described. Such an arrangement is the subject matter of a co-pending application Ser. No. 570,- 484 filed by O. P. McCarty and F. S. Urbanek on Aug. 5, 1966, and now issued as US. Letters Patent 3,472,981.

The latch release and relatching drive mechanism for the switch actuating rod 50 is best illustrated at FIGS. 4 and 6. This mechanism comprises a rocket shaft 60 having a pair of radial arms 62 and 63- and pivotally mounted in spaced-apart bearings 61 carried by the supporting panel 30. The arms 62 and 63 are fixed to the shaft 60 and, therefore, move in fixed relation to each other. The radial arm 62 is connected in positive driving relation to the actuating rod 50 by means of a pin and slot connection 62a, while the radial arm 63 is provided at its outer end with the latching shoulder 63a cooperable with a springpressed latch detent 64. The latching arm 63 and the latch detent 64 are provided, respectively, with laterally extending fingers 65 and 66 parallel to each other and to the rocker shaft 60. A bell crank lever 67 having one end coupled to the cam follower rod 28 is rotatably mounted upon the shaft 60 and disposed at its opposite end to cooperatively engage the latch arm and detent fingers 65 and 66 respectively.

As most clearly illustrated at FIG. 4, the bell crank lever 67 forms a one-way driving connection with the latch finger 65 so that when the bell crank 67 is moved in driving relation with the finger 65 the latch arm 63 and connected driving arm 62 are moved upwardly (as viewed at FIG. 4) to drive the switch actuating rod 50 vertically upward against the bias of the spring 51 and bring the latch finger 63 in latching relation with the detent 64. In addition, the bell crank lever 67 is provided at its outer upper end with a cam surface 67a engaging the detent finger 66 so that when the bell crank lever 67 is rotated in the opposite direction (counterclockwise as viewed at FIG. 4), the latching detent 64 is moved toward latch-releasing position while the bell crank lever 67 moves independently of the rocker shaft 60 and its connected radial arms 62 and 63. It will be evident that when the cam surface 67a acting upon detent finger 66 releases the mechanical latch 63a, 64, the latching arm 63 and driving arm 62 are released for sudden downward movement under the driving action of the actuating spring 51 acting upon actuating rod 50.

The mode of operation of my improved switch actuating and control mechanism will now be evident from the following brief description of a typical contact-opening and reclosing sequence for the vacuum interrupting device 14. Referring particularly to the perspective view at FIG.

4, the mechanism is shown in its circuit-closing position with the mechanical latch 63a, 64 engaged to hold the actuating rod 50 in its circuit closing position against the bias of the actuating spring 51. The movable switch member, or rod, 55 and connected contact rod 38 are in circuit-closing position as a result of the contact closing bias exerted by the switch bellows 40.

To separate the contacts of the vacuum interrupting device 14, the operating cam 21 is rotated either clockwise or counterclockwise and in either event the cam follower lever 28a is moved in a clockwise direction (FIGS. 3 and 4) to move the operating rod 28 in the trip direction indication on the drawing at FIG. 4. The bell crank lever 67 is accordingly moved in a counterclockwise direction independently of the latch arm 63 and driving arm 62, but in so moving the cam surface 67a drives the latch detent 64 toward releasing position. When the latch 63a, 64 is released, the actuating rod 50 is suddenly released and driven rapidly downward under the action of the actuating spring 51. After a limited amount of free travel the rod 50, through the cage 54, engages the shouldered switch rod 55, 55a with a hammer blow and drives the movable contact rod 38 to open position at high speed.

Movement of the moving contact rod 38 to contact opening position is opposed by the ambient fluid, which may be a dielectric liquid, trapped within the bellows 40. As previously explained the exhaust orifices 45 in the switch mounting plate 43 (FIG. 5) are so proportioned that this fluid will be exhausted from the bellows at the desired rate without imposing excessive stress upon the bellows. By properly proportioning the size of these orifices and the force of the actuating spring 51, the speed desired of opening and limited fluid pressure may be attained.

As previously explained, it is desirable to reclose the vacuum interrupter contacts 36, 37 at a speed less than the speed of opening. For this purpose a positive reclosing drive is provided through the bell crank lever 67, the driving arm 62 and the switch actuating rod 50. The speed of this reclosing movement is positively controlled by the speed of rotation of the operating cam 21 and the configuration of the cam slot 26. In such reclosing movement the cam follower lever 28a is positively moved in a counterclockwise direction by the cam 21 and positively moves the bell crank lever 67 in a clockwise direction. In so moving, the lever 67 releases the latch detent 64 for return to its latching position and positively engages finger 65 to drive the latch arm 63 and the driving arm 62 upward. When the driving arm 62 is thus positively driven upward at controlled speed, the actuating rod 50 is similarly moved upward. During the initial portion of this movement the shouldered switch member 55 is restrained against its contact closing bias by engagement with the upper portion of the cage 54 and is thus allowed to move toward closing position only so rapidly as the actuating rod 50 is moved. When the vacuum interrupter contacts come into engagement, up-

ward movement of the switch member or rod 55 ceases and the actuating rod 50, due to its lost motion cage connection with the rod 55, continues to move upward in an overtravel portion of its motion to the latching position shown at FIG. 4.

It will be understood by those skilled in the art that in the contact-closing movement described immediately above, the movable switch member 55 and connected moving contact member will move upward in following the interrupter bellows 40. For this purpose an additional closing spring may be provided as shown at FIG. 7. In that figure the movable switch rod 55 is provided with an additional shoulder 55band a compression spring 70 is positioned between that shoulder and the fixed bracket 52. It will of course be understood that in providing any such additional closing bias it is necessary that the opening force of the actuating spring 51 be considerably larger than the total closing bias applied to the movable switch member so that in opening operation the actuating spring 51 will positively overpower the total closing bias of the contact member.

It will now be understood that while I have illustrated a preferred embodiment of my invention by way of example, various modifications will occur to those skilled in the art. I, therefore, wish to have it understood that I intend in the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Electric switching apparatus comprising a vacuum type electric circuit interrupter having fixed and movable contact members mounted for closing and opening operation within an evacuated envelope, said envelope including a deformable wall portion sealed to said movable contact member and acting by diflerential pressure to bias said movable contact member to contact-closing position, said diiferential pressure constituting at least a major portion of a net closing bias normally constantly acting upon said movable contact member, a movable switch actuating member, lost-motion means loosely coupling said switch actuating member to said movable contact member for limited relative movement, said switch actuating member being movable from contact-opening position to contact-closing position with said movable contact member in following engagement under the influence of its closing bias and said lost-motion means permitting further movement of said switch actuating member in its contact-closing direction to an overtravel position, releasable mechanical latch means engaging and holding said switch actuating member in said overtravel position, an actuating spring connected to move said switch actuating member at high speed from said overtravel position to its contact-opening position against the closing bias of said movable contact member, said lost-motion means providing sudden impact to said movable contact member in contact-opening movement, and driving means positively connected to move said switch actuating member from its contactopening position to said overtravel position at a predetermined speed sufiiciently low to permit following engagement of said movable contact member to the limit of its contact closing movement.

2. A switching apparatus according to claim 1 wherein said driving means includes a driving member positively engaging said switch actuating member in one direction of movement and reversibly movable independently of said switch actuating member to release said mechanical latch means.

3. The combination with a switching apparatus according to claim 2 of a rotatable operating member movable in either direction from a predetermined rest position to actuate said driving member in one predetermined direction of movement and thereafter to reversely actuate said driving member in continued rotation toward said rest position.

4. A switching apparatus according to claim 1 in which said driving means includes a pivotally mounted latch member positively connected to said switch actuating member and having a portion engaging said releasable latch means, a pivotally mounted driving member movable in one direction to engage and drive said latch member to latching position and movable in the opposite direction independently of said latch member, said driving member including cam means operable in said op- 3,159,731 12/1964 Luebring 200l44.2 posite direction of movement to engage and release said 3,206,580 9/1965 McCarty 200144.2 latchmeans. 3,250,880 5/1966 Jennings 200144.2 X

5. A switching apparatus according to claim 1 where- 3,267,247 8/1966 Ross ZOO-144.2 X in a push-01f spring normally overcome by said differen- 3,383,484 5/ 1968 Arp et a1. 20083.1 tial pressure is connected to bias said movable contact 5 3,399,286 8/ 1968 Kerr 200144.2 member to circuit-opening position upon significant re- 3,319,121 5/ 1967 Lee ZOO-144.2 duction of said differential pressure. 3,025,375 3/1962 Frank 200144-2 References Cited 10 ROBERT K. SCHAEFER, Primary Examiner UNITED STATES PATENTS R. A. VANDERHYE, Assistant Examiner 2,472,625 6/1949 Smith 200144.2 X US CL 2,838,636 6/1958 Schwager i 200 1442 X 20Q 83, 153

3,038,980 6/1962 Lee zoo-144.2 15 

